This invention relates to occupancy sensors. More particularly, this invention relates to occupancy sensors that can operate for extended periods of time without an external power source.
Occupancy sensors typically sense the presence of one or more persons within a designated area and generate occupancy signals indicative of that presence. Such occupancy signals may then drive, for example, a low voltage transformer and relay to activate or deactivate one or more electrical devices or appliances, such as, for example, room lighting or an HVAC (heating, ventilating, and air conditioning) system. Occupancy sensors help reduce energy and maintenance costs by turning devices and appliances OFF when not needed.
Accordingly, occupancy sensors are typically used in a variety of commercial, industrial, and residential settings. Most known occupancy sensors require an external power source in order to operate. That is, they require a connection to an external power source in order to power sensing, timing, and switching circuits that turn lights or other devices ON and OFF in accordance with sensed occupancy. Thus, a disadvantage of most known sensors is that they cannot be used in areas where power is not readily available.
Furthermore, the settings mentioned above typically have different electrical environments. For example, some settings have AC line voltage that may be 120, 240, 277, or 347 volts. Other settings may have only DC voltage supplies available. Another disadvantage of known occupancy sensors is that they typically can operate only within a narrow range of either AC or DC input voltage. For example, many known sensors can only operate at 120 volts AC. Such sensors are not likely to operate at, for example, 12 volts DC or 240 volts AC. Similarly, an occupancy sensor that can operate at 24 volts DC, cannot likely operate at an AC line voltage of 347 volts. Thus, known occupancy sensors are generally limited to a particular input voltage range and type (AC or DC). Such voltage limitations can significantly limit the types of applications in which known occupancy sensors can be used.
Another disadvantage of known occupancy sensors is that they often waste power in standby mode (i.e., when the sensor is not sensing occupancy). Power is wasted because known occupancy sensors continuously draw current. Often, this continuously drawn current is set to the peak current of the sensor. Peak current, however, is only required when occupancy is sensed, which is when most circuit activity occurs. Thus, more power than necessary is often dissipated (and thus wasted) in known sensors. This can become notable, for example, in an office complex where dozens of such sensors are deployed.
Moreover, unnecessary power dissipation is usually higher in known occupancy sensors with relay outputs. Relay outputs advantageously allow a sensor to be used in many different types of applications. However, relay outputs typically consume relatively large amounts of current.
Sensors with relay outputs include a relay coil that is energized and de-energized as needed to switch the relay output to either couple power to a load (i.e., a device or appliance to be turned ON/OFF by the sensor) or decouple power from the load. Many known sensors maintain the coil in an energized state while in standby mode. This significantly increases power dissipation.
Another disadvantage of known occupancy sensors is that they are easily mis-wired during installation. Most sensors have wires for connection to the hot, neutral, and ground leads of a power source, and other wires for connection to a load and power source for the load (if different from the power source for the sensor). Wiring mistakes are common, typically causing installation delays and malfunctioning sensors, which may not always be immediately detected.
A further disadvantage of known occupancy sensors is that they usually require a warm-up period upon initial installation and after power outages. This also can delay installation because installers need to wait until warm-up is complete in order to ensure that sensors are functioning properly. Warm-up periods after power outages can also waste power because many known sensors warm up in the ON state. Thus, for example, lighting for a manufacturing floor may turn ON after power is restored at a time when no one is present. Conversely, other known sensors that warm up in the OFF state can further disrupt productivity after a power outage. For example, an occupied area may remain without lights or HVAC for the duration of the warm-up period after power is restored.
A few known occupancy sensors power some functions with a battery. For example, some sensors use the battery as backup in case of a power outage, to store data for later downloading to a computer, or to transmit a signal to a remote receiver. Battery-operated occupancy sensors, however, are not known to use a battery to operate a relay output which, as mentioned above, advantageously increases the versatility of the sensor. Furthermore, known battery-operated occupancy sensors typically cannot operate at extended periods of time without replacing the battery, thus maintenance costs may be higher for such sensors.
Some known occupancy sensors operate with rechargeable batteries. These sensors have additional disadvantages. For example, rechargeable batteries are usually more expensive than non-rechargeable batteries, have more internal leakage resulting in more rapid capacity loss, often require 24-48 hours of initial charging before the sensor is fully operational, typically require connection to a load in order to remain fully operational (the batteries leak current through the load while the load is off), and typically require a current transformer in series with the load in order to re-charge while the load is powered.
In view of the foregoing, it would be desirable to be able to provide an occupancy sensor that can operate for many years without an external power source.
It would also be desirable to be able to provide an occupancy sensor with a relay output that can operate for many years without an external power source.
It would further be desirable to be able to provide an occupancy sensor that dissipates very little power.
It would still further be desirable to be able to provide an occupancy sensor that is easily installed.